Apparatus for producing a ground or ground and polished continuous strip of glass



May 9, 1944. F. BQWALDRON 2,343,581

APPARATUS FOR PRODUCING A GROUND OR GROUND AND POLISHED CONTINUOUS STRIP OF GLASS klled Oct. 8, 1943 2 Sheets-Sheet 1 ttOrney-S May 9, 1944. F, B WALDRQN 2,348,581

APPARATUS FOR PRODUCING A GROUND OR GROUND AND POLISHED CONTINUOUS STRIP 0F GLASS Filed Oct. 8, 1945 2 Sheets-Sheet 2 W @440 Inventor S 8 I A itorn y s.

?aiented May 9, 1944 UNITED STATES PATENT OFFICE APPARATUS FOR PRODUCING GROUND OR GROUND AND POLISHED CONTINUOUS STRIP F GLASS Application October 8, 1943, Serial No. 505,476 In Great Britain October 31, 1942 Claims.

This invention relates to apparatus for producing a ground or ground and polished continuous strip of glass.

In the type of apparatus to which th invention is applicable, a strip of glass is formed from molten glass in a tank, is passed through a lehr and then through a grinding apparatus followed, if the strip is to be polished, by a polishing apparatus. In the grinding and polishing apparatus driving rollers are provided for driving the glass forward in a linear path, the rollers being spaced along said path and the tools are in coaxial pairs, usually one pair between each pair of driving rollers, the two tools of each pair operating opposite to each other on the upper and lower surfaces of the strip. The lower tools are usually adjusted in height so that the series of tools form a plane surface on which the strip rests, while the upper tools are provided with manually controlled devices adapted when operated either to raise a tool from, or to lower a tool down on to, the strip.

The strip is normally continuous from the forming apparatus to the further end of the grinding or grinding and polishing apparatus, but from time to time the strip cracks across in its passage through the apparatus. The fact of the strip being non-continuous by reason of such a crack does not per se interrupt the continuous operation of the apparatus, because the strip is driven through the apparatus by pairs of rollers between each pair of tools, and the two lengths of strip are driven independently through the apparatus.

In the processes of grinding and polishing a continuous strip of glass in which both surfaces are ground or polished simultaneously, it is of the utmost importance that the occurrence of a crack in the glass should be ascertained within a very short time. If a length of glass following a crack is allowed'to reach a pair of grinding tools, the glass is broken up and a considerable quantity is wasted. If it is allowed to reach a pair of polishing tools, the polishing felts are damaged by the sharp edges of the glass. Moreover if a crack occurs in the length of glass being operated on by a pair of tools, the glass is liable to be broken up or the polishing felts are liable to be damaged.

The main object of the present invention is a device whereby an operating tool in the vicinity of a crack may be raised, either manually or automatically in the shortest possible time after a crack has started.

It has been found that the cracking of a strip of glass in a grinding and polishing apparatus emits a noise consisting of a damped wave train of short duration of frequencies higher than those in the bulk of the general noise of the grinding and polishing apparatus, but that this general noise does contain continuous waves of frequencies of the same order as those emitted by the cracking glass, but of lower intensity.

According to the invention a method of controlling machinery used in grinding or polishing simultaneously the two surfaces of glass in continuous strip form, consists in utilising the brief train of sound waves emitted by the cracking of the glass to operate a microphone device which, when set into vibration, emits an electrical impulse to a relay, the relaybeing employed to operate an automatic device for raising a tool operating on the upper surface of the glass or to operate a signal device to draw the operators attention to the existence of the crack in the glass, or both; the microphone device being of low inertia adapted to respond to a brief train of sound waves of frequencies of the order of those emitted by the cracking of the glass, but not to respond to sounds of other frequencies accompanyingthe processes of grinding and polishing, and being adjusted in sensitivity so as not to respond to the low intensity sounds accompanying the said processes which are of frequencies of the order of those emitted by a crack.

The vibratory element may be comprised in a microphone which is tuned to respond to the desired band of frequencies and, when set in vibration operates a relay such as a grid controlled gas-filled valve. Alternatively the microphone may respond to frequencies other than those of the desired band and may supply varying current to an electric circuit adapted substantially to cut out frequencies below those of the desired band, or may supply the varying current to a valve amplifier adapted to amplify the desired band of frequencies. The filtered or the amplified electrical impulse resulting from the sound wave emitted by the crack is caused to operate a relay. The term cut out is intended to include reducing to an intensity which can be neglected.

The relay may operate an automatic device to raise one or more of the grinding or polishing tools operating on the upper surface of the glass, in. the neighbourhood of the crack, so as immediately to raise them from the glass, and preferably also to stop immediately the rotation of the lower tools, and if desired the upper too1s.also.

In one preferred embodiment, a series of microphones or microphone devices are placed near the glass at intervals along the strip, and the intervals are conveniently given the same spacing as the spacing of the tools.

Each vibratory element employed must be of small enough inertia to respond adequately to the brief train of sound waves of high intensity, and then the sensitivity of the device may be adjusted so that its does not respond to the cumulative eifect of the continuous wave of high pitch forming part of the general noise.

The response to the sound of a crack may, generally, be restricted to a single one of the series of microphone devices, by adjusting the sensitivity of the devices and by acoustic screening between adjacent microphones. In some constructions the grinding or polishing apparatus comprises frames carrying the driving rollers and supporting the superstructure, these frames dividing the apparatus into successive bays in which the tools operate, each frame carrying also a vertical curtain to prevent rouge from splashing over from one bay to the next, and each bay being decked over horizontally. In apparatus of this form the microphones, placed one in each bay, are, to a great extent, screened from one another by the driving rollers and their frames and by the curtains and decking.

If desired the circuits of the microphones may be so interconnected that energisation of the relay associated with one microphone renders effective the means for energising the relay associated with the next succeeding microphone and maintains inefiective the means for energising the relay associated with the next microphone but one, whereby the response of one microphone causes the raising of the tool associated with the microphone which has responded and also the next succeeding tool, but not subsequent tools. I

In order that the invention may be more fully understood one embodiment thereof will now be described by way of example with reference to the accompanying diagrammatic drawings.

In the drawings:

Figure 1 illustrates in plan one form of polishing installation according to the invention, for use in surfacing plate glass of 6 to '7 mm. thick;

Figure 2 shows in elevation and to a larger scale two adjacent bays of the installation, each containing a pair of tools and a microphone;

Figure 3 is a diagram of the electrical control circuit associated with one microphone employed in the installation shown in Figures 1 and 2, and

Figure 4 shows a circuit whereby response of a microphone in one bay raises the upper tool in that bay and also the tool in the next succeeding bay, but not the tools in subsequent bays.

In the drawings like references designate the same or similar parts.

In the construction shown in Figures 1 to 3 the installation comprises a plurality of equally spaced co-axial pairs of polishing tools I of known form of which three pairs are indicated in Figure 1 and two pairs only shown in Figure 2 and pairs of rollers 3 (Fig. 2) for driving the glass strip 2 in a horizontal path between the pairs of tools, the rollers being spaced along said path. Only the upper tool I of each pair is visible in Figure 1, the lower tool being on the lower side of the strip 2 immediately below the upper tool.

Each tool I is rotated by a vertical shaft 4 and the shafts of the two tools of a pair are in line.

Each pair of rollers 3 is carried in afixed vertical portion of the framework of the apparatus.

said vertical portion including two columns 5 and a transverse member 5a, successive vertical pottions of the framework dividing the apparatus into successive bays B (Figure 2) in each of which there is disposed a pair of rotating tools I.

In each bay B there is hung from the transverse member 5a, by means of a known form of suspension indicated at 6 in igure 2, a microphone 1 directed inwardly of the bay, the suspension being such as to dispose the microphone as near as possible to the glass strip, and the spacing of the microphones being the same as that of the tools.

Extending across the columns 5 of each bay is a vertical curtain 5b and each bay is also provided with horizontal decking, indicated at 50.

Each of the microphones indicated at I is of small enough inertia to respond adequately to the brief train of sound waves of high intensity emitted by the cracking of the glass, and controls the supply of current to the electrical circuit shown in Figure 3 which, as described later, includes a filter l3 adapted to cut out frequencies below 1500 cycles per second and to pass frequencies of the order of those of the sound of glass cracking in the installation.

The microphone 'l is adjusted in sensitivity so as not to respond to the low intensity sounds accompanying the process of polishing which are of frequencies of the order of those emitted by a crack.

Experiments have shown that by employing a 'microphone which responds to a frequency above 1500 cycles per second with an electrical circuit adapted to cut out frequencies below 1500 cycles per second, the device when suitably adjusted in sensitivity will respond to the noise of a crack and not respond to the general noise of a grinding and polishing operation.

Accordingly the microphone I with valve circuit and filter I3 together constitute a microphone device adapted to respond to the brief train of sound waves of frequencies of the order of those emitted by the cracking of the glass but not to respond to the sounds of other frequencies accompanying the grinding and polishing process and adjusted in sensitivity so as not to respond to the low intensity sounds accompanying the said process which are of frequencies of the order of those emitted by a crack.

Each microphone circuit may conveniently be arranged as shown in Figure 3.

One terminal of the microphone l is connected to the negative high tension line In and the other terminal to the grid of a first amplifying valve H of which the anode is connected through coupling condenser I2 and the filter l3 to the grid of a second amplifying valve I4.

Through'coupling condenser IS the anode of valve I4 is connected to the grid of a grid controlled gas filled valve l6 controlling the circuit of a relay coil II, the grid of said valve being biased to render the valve normally non-conductive.

The normally open relay contacts Ila are in the circuit of a contactor coil l8 and serve, when closed, to complete the circuit from the A. C. mains through the contactor coil.

The contactor includes normally open contacts l8a, which, when closed establish a holding circuit for the coil l8, normally open contacts "b controlling the supply of current to a pair of terminals I9, lSa across which may be connected an electrical device for giving an indication of the presence of a crack in the glass strip 2, and normally closed contacts [8c in series with the relay coil I! in the anode circuit of the gas filled valve I8.

When the sound of glass' cracking in the installation is picked up by the microphone 'l the resulting electrical impulse, amplified by the valve II is passed by the filter I3 to the second amplifying valve I4 whence it reaches the grid of the gas filled valve I6.

The characteristic of the valve I6 is such that the amplified impulse from the microphone causes the valve to fire and conduct current, which continues to flow after the impulse from the microphone has ceased. This current energises relay I! which closes its contact I Ia thereby establisliing the circuit through contactor coil I8 which closes its contacts la and I8b and opens its contacts I80.

Closure of contacts I8a establishes the holding circuit for the contactor coil I8 and closure of contacts I8b energises the circuit containing the terminals I9, I9a, while opening of contacts I80 breaks the anode circuit of the gas filled valve I8 so that the current flow through this valve and the relay coil II ceases. Contactor coil I8, however, remains energised through the holding circuit which is maintained through contacts I8a.

It will be understood that the arrangement must be such that the contacts I8a. close to establish the holding circuit for the contactor coil I8, before the contacts I8c open to break the anode circuit of the valve I6. 7

The electrical device which is connected across the terminals I9, I9a, may be a lamp 20 as shown in Figures 1 and 3 for giving a visual indication of the presence of the crack, or it may be a device for giving an audible indication. Thereby the operator is advised of the position of a crack as soon as it occurs and is able quickly to raise the upper tool operating on the length of glass in the .bay in which the crack is, and to stop the operation of the lower tool. Similarly an operator can, on hearing or seeing a signal, relieve the pressure applied to the glass by the top rollers of a driving pair disposed between the operating tools.

Preferably, however, as also shown in Figures 1 and 3, the relay H in addition to or instead of controlling a signal, for example the lamp 2!], serves to control automatic means for raising the upper tool from the glass strip 2.

Each shaft 4 carrying the upper and lower tools is, in the example shown, driven in the usual manner from an independent motor 2I through worm gearing 22, a pinion 23 and a spur wheel 24 secured to the associated driving shaft 4 (see Figures l and 2).

The upper tool is provided in the known manner with automatic means for raising it clear of the glass, and a motor driven form of automatic means is shown diagrammatically in Figures 1 and 2 wherein the shaft 4 for the upper tool is mounted in a sleeve 25 which is disposed to slide vertically on the fixed frame F and carries a lateral extension 26 having an internally screw threaded bore with which engages a screw threaded spindle 21 of which the lower end bears on the frameF. Secured to the spindle 21 is a bevel wheel 28 meshing with a bevel wheel 29 secured to the shaft of a motor 30 (Figure 1).

In order to operate the raising means automatically immediately a crack is detected by the microphone I, the motor 30 is connected in series with the terminals I9, I9a, so that when the contacts I8b controlled by coil I8 close due to a crack in the glass, the motor 30 revolves so as to rotate the spindle 21 in a direction to raise the sleeve 26 and therefore the upper tool I clear of the glass strip 2.

The usual safety switch is providedin the motor circuit which is opened when the sleeve 25 reaches the limit of its travel.

The terminals I9, I91: may also be connected to a contactor switch 3| (Figure 2) serving to control the current supply to the driving motor 2| for the lower tool in such a way as to stop the rotation of the lower tool by cutting off the current supply to its motor when the circuit of the terminals I9, I91: is interrupted.

When the apparatus is ready for starting again the operator de-energises the contactor coil I8 by opening a resetting switch 32 which is preferably of the press-button type. Thereupon contacts I8a and I8b open and contacts I8c close, so that upon release of the press button switch 32 the relay circuits are restored to normal condition, in which they are again available for operation.

In a modified arrangement the first amplifying valve II and the filter I3 may be replaced by a valve amplifier tuned to frequencies of the order of those of the sound of glass cracking in the installation,

In an alternative modification, the microphone device may comprise, instead of the microphone 1 and filter I3, a microphone which is tuned to respond to the band of frequencies of the sound of cracking glass and not to low frequencies, in which case the filter I3 will be dispensed with, the microphone being connected through amplifying valves such as II and I4 to the gas filled valve IIi.

Where automatic motor driving means is provided for raising the upper tools each contactor I8 may include two further contacts shown in chain lines at Mid and I8e in Figure 3, and in full lines in Figure 4. The contacts I811, normally open are in series with the contacts I8e of the contactor I8 in the preceding bay B, and this circuit shunts the relay contacts IIa associated with the microphone 1 in the next succeeding bay.

On energisation of a coil I8 associated with any bay B in which a crack has occurred the contacts I8d will close and, through contacts I8e of the contactor for the preceding bay, will energise the coil I8 for the next succeeding bay whereby the upper tool raising motor for said next succeeding bay will be actuated as well as the motor for raising the upper tool in the bay in which th crack has occurred. By this means damage to thepolishing felts in the next succeeding bay B due to the broken glass reaching them, before the operator has had time to operate the tool raising motor personally, is avoided.

Energisation of coil I8 in the next succeeding bay will, of course, close the associated contacts I8d but this is prevented from energising the coil I8 in the next bay but one by the opening of contacts I8e of the contactor associated with the bay in which the crack has occurred, which contacts I8e are in series with the contacts IBd of the contactor in the next succeeding bay. Accordingly only the tools in the bay in which the crack has occurred and in the next succeeding bay are raised, the remaining tools being unaffected.

By the present invention apparatus is provided which is adapted to prevent damage arising out of a crack in the glass, sincea tool over or con tiguous to the crack may be raised very soon after the crack occurs, and thereby a visible indication of the existence of a crack is called to the attention of an operator, although as herein referred to, an audible signal may also be caused to occur.

I claim:

1. A method of controlling machinery used in surfacing simultaneously the two surfaces of glass in continuous strip form, consisting in utilising the sound waves emitted by the cracking of the glass to operate a low inertia microphone deviee which, when set into vibration emits an electrical impulse to a relay, the relay being employed to operate an automatic device for giving an indication of the existence of a crack in the glass, restricting the response of the microphone device to frequencies of and above the order of those emitted by the cracking of the glass, and adjusting the sensitivity of the device so that it does not respond to the low intensity sounds accompanying the said process which are of frequencies of the order of those emitted by a crack.

2. Apparatus for controlling machinery used for surfacing glass, of the kind wherein a continuous strip of glass travels between a plurality of pairs of rotary tools operating simultaneously on the two surfaces of the strip, comprising in combination a microphone device responsive to sound waves of frequencies emitted by the cracking of the glass, but not to the sound waves of lower frequencies emitted by the surfacing process, and of a sensitivity insufficient to allow it to respond to the low intensity sound waves emitted by the said process which are of frequencies of the order of those emitted by a crack, a relay, electrical connections between the microphone device and said relay whereby the ielay is controlled by electrical impulses emitted by the microphone device and means operative under the control of the relay, when energised, to give an indication of the existence of a crack.

3. An installation for surfacing glass of the kind wherein a continuous strip of glass travels between a plurality of pairs of rotary tools operating simultaneously on the two surfaces of the strip, and including power driven means for raising each upper tool from the glass, comprising in combination a plurality of microphone devices, each including a microphone, said microphones being placed near the glass at intervals along the strip and said intervals being given the same spacing as the spacing of the tools, acoustic screening means disposed between adjacent microphones for restricting the sound of a crack to a single one of said microphones, a relay appropriated to each microphone device, electrical connections between each relay and its appropriated microphone device whereby each relay is controlled by impulses emitted by said microphone device, means actuated by each relay, when energised to set into operation the power driven means for raising from the glass the tool appropriated to said relay, an electrical connection between the relay appropriated to one microphone and the relay appropriated to the next succeeding microphone such that energisation of one relay effects energisation of the next succeeding relay also, and an electrical connection between each relay and the next relay but one such that energisation of one relay renders ineffective the next relay but one, whereby the response of one microphone causes the raisin of the upper tool appropriated to the microphone which has responded and also the next succeeding tool, but not subsequent tools, each of the microphone devices being of low inertia adapted to respond to sound waves of frequencies of the order of those emitted by the cracking of the glass, but not to respond to sounds of other frequencies accompanying the surfacing process, and being adjusted in sensitivity so as not to respond to the low intensity sounds accompanying the said process which are of frequencies of the order of those emitted by a crack.

4. An installation for surfacing glass of the kind wherein a continuous strip of glass travels between a plurality of pairs of rotary tools operating simultaneously on the two surfaces of the strip and including in combination a framework having successive fixed vertical portions spaced along the path of the glass and dividing the apparatus into successive bays, a pair of horizontal rollers carriedin each vertical portion of the framework, said rollers serving to drive the glass forward in a linear path, a curtain carried by each vertical portion of said framework and extending above the rollers, horizontal decking extending between adjacent vertical frame portions to form a covering to the bay constituted therebetween, a pair of rotating surfacing tools disposed in each bay, the tools of each pair operating the one on the upper face and the other on the lower face of the glass,

- and means for driving said tools, a microphone device to each bay and including a microphone located within the bay and facing a free area of the glass strip, a relay appropriated to each microphone device, electrical connections between each relay and its appropriated microphone device whereby the relay is controlled by electrical impulses emitted by the microphone device, and means operative under the control of each relay to give an indication of the existence of a crack, each of the microphone devices being of low inertia adapted to respond to sound waves of frequencies of the order of those emitted by the cracking of the glass, but not to respond to sounds of other frequencies accompanying the surfacing process, and being adjusted in sensitivity so as not to respond to the low intensity sounds accompanying the said process which are of frequencies of the order of those emitted by a crack.

5. An installation for surfacing glass of the kind wherein a continuous strip of glass travels between a plurality of pairs of rotary tools operating simultaneously on the two surfaces of the strip and including in combination a framework having successive fixed vertical portions spaced along the path of the glass, and dividing the apparatus into successive bays, a pair of horizontal rollers carried in each vertical portion of said framework, said rollers serving to drive the glass forward in a linear path, a curtain carried by each vertical portion of said framework and extending above the rollers, horizontal decking extending between adjacent vertical frame portions to form a covering to the bay constituted therebetween, a pair of rotating surfacing tools disposed in each of said bays the tools of each air operating the one on the upper face and the other on the lower face of the glass, means for driving said tools, and power driven means for raising each upper tool from the glass, a microphone device to each bay and including a microphone located within the bay and facing a free area of the glass strip, a relay appropriated to each microphone device, electrical connections between each relay and its appropriated microphone device whereby the relay is controlled by electrical impulses emitted by the appropriated microphone device, and' means actuated under control of each relay, when energised, to set into operation the power driven means for raising from the glass the upper tool in the appropriated bay, an electrical connection between the relay appropriated to one microphone and the relay appropriated to the next succeeding microphone such that energlsation of one relay effects energisation of the 5 next succeeding relay also, and an electrical connection between each relay and the next relay but one such that energisation 01 one relay renders ineffective the next relay but one, whereby the response of one microphone causes the 10 raising of the upper tool appropriated to the microphone which has responded and also the surfacing process, and being adjusted in sensitivity so as not to respond to the low intensity sounds accompanying the said process which are of frequencies of the order of those emitted by a crack.

FREDERIC BARNES WALDRON. 

